Reflective Surface Measurement Using Differential Geometric Deflectometry
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Solution Overview
Problem
Existing methods for optical measurement of reflective and partially reflective surfaces face challenges such as height ambiguity, requiring complex setups, additional equipment, and high costs, which are not practical for full-surface measurements.
Innovation Solution
A method combining phase-measuring deflectometry with differential geometric approaches using a pattern generator to create a planar pattern with varied optical properties, allowing full-surface measurement with minimal equipment by determining geometric properties through a correspondence function and differential geometric transformations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If phase-measuring deflectometry is used to measure reflective surfaces, then full-surface measurement capability is achieved, but height ambiguity occurs making surface normal determination impossible without additional information
Solution Approach 1:
The patent introduces a calibration object with a known reference surface as an intermediary element. This calibration object serves as a mediator between the camera system and the target reflective surface, providing known reference points that enable the system to resolve height ambiguity and determine accurate surface normals without requiring additional active sensors on the target object itself
Solution Approach 2:
The patent performs preliminary calibration measurements using a calibration object with known geometric properties before measuring the actual target surface. This preliminary action establishes reference data and calibration parameters that are then used to resolve height ambiguity during subsequent measurements of reflective surfaces
2Measurement precision
If additional cameras or displacement mechanisms are added to resolve height ambiguity, then measurement accuracy improves, but device complexity and costs increase
Solution Approach 1:
The patent uses a calibration object that creates a known reference pattern or 'copy' of geometric information. This reference copy provides the necessary height and orientation data without requiring physical copies of the target object or additional measurement systems, thereby avoiding increased device complexity while still resolving height ambiguity
Solution Approach 2:
The calibration object serves multiple functions: it provides reference points for height determination, establishes coordinate system alignment, and enables camera calibration all in a single element. This multi-functionality eliminates the need for separate displacement mechanisms or additional cameras, reducing overall device complexity
3Measurement precision
If screen position is shifted perpendicular to the screen plane to determine radiation direction, then height ambiguity is resolved, but measurement time increases and complex mechanics are required
Solution Approach 1:
The patent performs the function of determining radiation direction through preliminary calibration with a known reference object rather than through time-consuming sequential measurements at multiple screen positions. This preliminary calibration stores reference data that is then used during actual measurements, dramatically reducing measurement time while maintaining accuracy
Solution Approach 2:
The patent replaces the mechanical screen shifting mechanism with a computational approach using known geometric relationships from the calibration object. Instead of physically moving the screen to determine radiation direction, the system uses mathematical calculations based on the known calibration reference, eliminating complex mechanics and reducing measurement time
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables full-surface optical measurement with reduced equipment and costs, providing accurate geometric properties like height, inclination, and curvature without additional cameras or displacement mechanisms.
Implementation Method 1
at least the parts of the pattern are reflected by a reflective surface of the object as a reflected pattern onto the detector of the camera unit
Data Source
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AI summary
The invention relates to a method for optically measuring an object having a reflective and/or partially reflective surface. According to the invention, by means of a pattern generator (1), a planar pattern (13) is generated which is varied in at least one optical property such that, at least in partial regions (10), a plurality of different points (p) or a plurality of different groups of points are distinguishable from each other. At least parts of the pattern (13) are reflected by a reflective surface (2) of the object (3) as a reflected pattern onto a detector (14) of a camera unit (4), wherein the reflected pattern is converted by the detector (14) into a camera image (9). A connection between points (q) of the camera image (9) and corresponding points (p) of the pattern (13) can be described by means of a correspondence function which is dependent on geometric properties of the reflective surface (2) of the object (3). At least one of the geometric properties of the reflective surface (2) of the object (3) is determined by using differential geometric properties of a transformation given by the correspondence function. The invention furthermore relates to a corresponding system and a corresponding measuring arrangement.